Oxidation of alkali metals



Jan. 14, R R MILLER OXIDATION OF ALKALI METALS Filed Sept. 15, 1942 /A/. lfA'L ME 7341.

ROMAN RMILLER m WWW/J Patented Jan. 14, 1947 2,dli,lld

GXIBATIGN F ALKALI METALS (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) Claims.

This invention relates to the oxidation of alkali metals, and it is particularly directed to a method of preparing potassium tetrcxide and mixed higher oxides of sodium and potassium.

It has long been known that various alkali metal higher oxides are capable of giving up oxy gen to the air, under certain conditions, and also of absorbing carbon dioxide to 9. greater or less extent. Therefore, these materials are used in breathing equipment designed either to protect the user from toxic gases or to purify or regencrate a limited supply of air. Of the various higher oxides the most eilicient from the standpoint of avae oxygen per weight of the oxide is potassium tetroxide. Sodium peroxide yields less oxygen but it generally reacts more quickly, in the beginning of the reaction, with moisture in the air, possibly due to the formation of hydrates. Accordingly it is common practice to use a mixture of potassium tetrox" (K204) and sodium peroxide (NazGz) eoui out for air regeneration although the pure potassium tetroxide can be used alone to yield a greater quantity of oxy- It has heretofore been difficult to prepare potassium tetroxide, sodium peroxide and mixtures thereof pure form on a commercially practicable sea Various methods which have been include dissolving the alkali metal in liquid ammonia and bubbling oxygen through the solution, and of course burning the metals and their alloys in either liquid or solid form in air or pure oxygen. The former method yields a fairly pure product but it is very expensive, requLes rigid control and presents an explosion haz" rd in the unavoidable gaseous mixture of ammonia and oxygen. The latter method, on the other hand, avoids the hazards and costliness of the former, but itis virtually impossible to obtain a pure product. At best a mixture of higher and lower oxides is produced, often including tiny particles of the unburned metal in the oxide ash.

This invention provides a method of preparing the alkali metal higher oxides substantially free from lower oxides and metal, simply and economically, Without the attendant hazards of the prior known processes of preparing the pure material. the higher oxides (e. g. K204 and N .09 may be obtained in pure form or in ade with one another. The method of this inv ltion is particularly useful for the preparation of potassium tetroxide.

The process of this invention comprises the direct oxidation of the alkali metal in vapor form by bringing the metal vapor directly into contact with oxygen, and in practice it is most convenient to bring the metal vapor into contact with an excess of air (which may be further diluted or enriched with oxygen) so that all of the vapor will be oxidized to the highest oxide. Although the oxidation may be carried out at reduced or increased pressure there is no advantage in doing so, and the temperature of the metal vapor (before burning) is most conveniently regulated by employing different concentrations of an inert gas, such as nitrogen, to carry the vapor into the burning chamber, if operation at the boiling point of the metal is not desired. However, in the preferred form of the invention the metal or mixture of metals (particularly a mixture of sodium and potassium) is vaporized at the boiling point.

In order that the invention may be more clearly understood a typical operation for the oxidation of potassium is described, with reference to the accompanying drawing.

In the drawing, potassium metal is melted in a heated reservoir Ill and the liquid metal flows through a conduit ll, controlled by a valve l2,

'' into a furnace iii. The furnace l3 consists of an iron chamber l4 electrically heated by a coil l5 and covered with heat insulation l6. In the furnace 53 the potassium is vaporized and the vapor removed by passing nitrogen into the chamber i l through a conduit IT. The nitrogen is pre-- heated in the conduit ll, by means of a heating coil is, in order to prevent condensation of potassium vapor as it is removed for burning. The mixture of nitrogen and potassium vapor passes through an exit tube l9 which is also heated by a coil Ell to prevent condensation of potassium. From the exit tube It the nitrogen and potassium vapor pass into a burning chamber 2| into which air is introduced through a conduit 22. As the air and potassium vapor meet the latter immediately ignites and burns to the tetroxide which appears as an extremely fine, fiufiy powder, most of which settles slowly as the nitrogen and unused air pass out of the burning chamber 2|. Some of the tetroxide is so finely divided that it remains as a smoke, and it is removed as the exit gases leave the chamber 2| and pass through a conventional Cottrell precipitator 23. By scraping the sides of the precipitator 23 periodically the tetroxide particles are caused to fall into a collecting vessel E l. The unused air and nitrogen pass out of the system through a vent 25. Other collecting means than a Cottrell precipitator may be employed to collect the oxide. A series of collecting drums or entrainment traps have been successfully used, especially in large scale operation.

It is desirable, although not essential, that the nitrogen used to carry the potassium vapor from the chamber I l be free from oxygen, for if even small amounts of oxygen are present there is a tendency for potassium tetroxide to build up in the exit tube l9 and eventually plug it up. It is essential that both the nitrogen and the air used for burning the potassium be as free as possible of moisture, as otherwise the tetroxide will be contaminated with lower oxides and sometimes potassium hydroxide. Similarly these gases should be free of carbon dioxide if the presence of carbonates in the product is to be avoided. Other inert gases may be employed instead of nitrogen, such as helium, but nitrogen is most practically obtainable. If desired the nitrogen may be dispensed with and pure potassium vapor brought into contact with the air in the burning chamber.

Above about 500 C. the vapor pressures of the alkali oxides increase fairly rapidl with temperature and in the case of potassium it reaches 760 millimeters (the boiling point) at 760 C. Therefore it is most practicable to operate the furnace l3 at some temperature above about 500 C., and for large scale operation the most satisfactory operating temperature is the boiling point of the alkali metal or mixtures of alkali metals. This is particularly true for mixtures of sodium and potassium. However, the precise operating temperature which is most eificient for a given installation depends on a number of engineering factors, such as furnace size, cost of fuel for heating, etc., and it is easily determined by those skilled in the art.

Similarly sodium metal may be substituted for the potassium referred to in the above operation, and, as already indicated, mixtures or alloys of sodium and potassium may be employed, the composition of which depends on the proportion of potassium and sodium oxides desired in the product; The process is particularly adapted for the oxidation of the sodium-potassium vapor mixtures obtained by the decomposition of molten potassium salts by contact with sodium metal,

as the vapors may be led directly from the reaction zone to the burning chamber.

Many other variations will be apparent to those skilled in the art and the invention should not be limited other than as defined by the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. Process for making alkali metal higher oxides which comprises vaporizing the alkali metal, carrying the vapor away from unvaporized metal by means of an inert gas, bringing the vapor into contact with oxygen and collecting the alkali metal oxide thus formed.

2. Process for making alkali metal higher oxides which comprises vaporizing the alkali metal, carrying the vapor away from unvaporized metal by means of a stream of nitrogen, bringing the mixture of nitrogen and alkali metal vapor into contact with dry air and collecting the alkali metal oxide thus formed.

3. Process for making mixed sodium and potassium higher oxides which comprises vaporizing a mixture 01" sodium and potassium metals, carrying the vapor mixture away from unvaporized metal by means of a stream of nitrogen, bringing the vapor mixture and nitrogen into contact with dry air and collecting the mixed oxide thus formed.

4. Process for making potassium tetroxide which comprises vaporizing potassium metal, carrying the vapor away from unvaporized metal by means of a stream of nitrogen, bringing the mixture of vapor and nitrogen into contact with dry air and collecting the oxide thus formed.

5, Process for making sodium peroxide which. comprises vaporizing sodium metal, carrying the vapor away from unvaporized metal by means of a stream of nitrogen, bringing the mixture of vapor and nitrogen into contact with dry air and collecting the oxide thus formed.

ROMAN R. MILLER. 

